Joint Channel Impulse Response and Noise-Variance Estimation for OFDM/SDMA Systems Based on Expectation Maximization

A joint channel impulse response (CIR) and noise-variance estimation scheme is proposed for multi-user Multiple-Input-Multiple-Output (MIMO) Orthogonal Frequency-Division Multiplexing/Space Division Multiple Access (OFDM/SDMA) systems, which is based on the Expectation Maximization (EM) algorithm. Multiple users communicating over time-invariant and/or time-variant channels are considered in this paper. Channel estimation becomes quite challenging in this scenario, since an increased number of independent transmitter-receiver links having different statistical characteristics have to be simultaneously estimated for each subcarrier. The proposed EM-based joint CIR and noise-variance estimator designed for multi-user MIMO OFDM/SDMA system is shown to simultaneously estimate the time-invariant and time-variant CIRs as well as noise-variance.